FLT180a is an experimental gene therapy being developed by Freeline to treat hemophilia B.

How FLT180a works

Hemophilia is a blood disorder in which patients do not make enough of a clotting factor. This means their blood does not clot as quickly as it should. For patients with hemophilia type B, the missing clotting factor is factor IX. This is because the patient has a mutation in the gene that encodes for factor IX, preventing the protein from being made or functioning normally.

Patients can have mild, moderate, or severe hemophilia, depending on how much clotting factor they produce. Gene therapies are being investigated as a method of treating patients with severe hemophilia, that is, patients who produce almost undetectable amounts of clotting factor without treatment.

FLT180a is a gene therapy that uses an inactivated virus (which does not cause disease or illness) to transfer a piece of DNA containing the information necessary to make factor IX into the liver cells of the patient. These are the cells that normally would produce factor IX. Once the DNA is inside the cell, it is inserted into the chromosomes of the patient and is processed normally to produce protein, in this case, factor IX.

There are still some unknowns about this treatment, primarily regarding side effects and how long the treatment will last.

FLT180a in clinical trials

A Phase 1 clinical trial (NCT03369444) is recruiting patients with hemophilia B in the United Kingdom to test FLT180a. Up to three different doses of FLT180a will be tested in 18 patients with severe hemophilia B.

A second Phase 2/3 study (NCT03641703) also is recruiting up to 50 participants in the same location to investigate the long-term safety and durability of factor IX activity in patients who have been treated with FLT180a gene therapy. Participants will be followed until they reach age 15 after the treatment. They will undergo procedures including physical examinations, blood tests, and liver ultrasounds. Participants also will need to complete a diary to document the occurrence of bleeding episodes and record the amount of factor IX concentrate they receive. Patient outcomes, including quality of life, disability, and physical activity, also will be recorded.

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